Semiconductor wafers are produced by complicated multi-step processes. The production of sophisticated electronic chips from wafers may include as many as about 150 steps. Technologies in the submicron range are very delicate, and there always exists a chance of error or malfunction at each of the many stages, which ought to be discerned as soon as possible. Inspection during the production process and at its end is an imperative stage of the production process and there exists a real need for effective inspection means, capable of inspecting a large number of wafers in an accurate manner within a reasonable time period.
Automated devices are developed in the 1960s, and it was customary to inspect the wafers after each production step by means of an optical microscope by an operator, In the 1970s the process was automated to a certain degree and automatic means were provided for transporting the wafers from a cassette to the inspection stage, with a precision stage position of autofocus inspection, classification of the wafer and its insertion into a specific cassette according to the grading of the specific wafer.
This enabled the operator to concentrate on the inspection itself without wasting time or concentration on the handling. Such automation increases the number of wafers that can be inspected per unit time and also improves the overall accuracy and reliability of the inspection by the human operator.
Automatic handling systems were further developed and are currently available from several manufacturers with extra features such as accumulation of defects statistics and automatic differentiation of the inspected wafers for accept, reject, and redo-stations.
Further development in the fields of inspection was the introduction of automatic inspection machines which analyze the inspected wafers and determine the defect location automatically. The task of the operator is thus minimized to classification of the defects and determination of their severity. Some machines are available in this group with prices typically over $750,000 each.
The gap between the automatic handling systems and the heavy duty automatic inspection systems is the field of our invention.